Subaru recommends replacing your drive belts (not timing belt) every 60,000 miles or so, so it sounds like yours may be in need of changing. Spraying a can of belt dressing on squealing belts is NOT a good idea. My brother's 98 Dodge Dakota pickup had squealing belts and the belt dressing didn't fix the problem - it just made a huge mess under the hood from the belts spraying the stuff everywhere. Also, +1 to the belt tensioner being a common failing part.
07 WRX (Albins 5MT + Blouch 20G)
Jorge Carrillo Tuned (365 whp/340 wtq)